1. Field of the Invention
The present invention relates to a speaker apparatus, and more particularly, to an improvement for realizing a reduced thickness of a speaker apparatus by reducing a dimension in an axial direction thereof.
2. Description of the Related Art
FIG. 1 shows a conventional construction of an general type of an electrodynamic speaker apparatus.
This speaker apparatus 1 is configured with a magnetic circuit 3, a frame 5 to which the magnetic circuit 3 is attached on a rear end, a cone-shaped diaphragm 9 having a peripheral roll-shaped edge 7 fixed to a diaphragm supporting portion 5a, which is a front end of the frame 5, and a voice coil 12 wound on a cylindrical voice-coil bobbin 11.
The magnetic circuit 3 is configured with a yoke 15 having a structure in which a cylindrical center pole 15b is projected from a center of a disk-shaped plate 15a, a ring-shaped magnet 16 loosely fitted on a periphery of the center pole 15b, and a ring-shaped top plate 17 equipped to be loosely fitted on a front edge of the center pole 15b so as to hold the magnet 16 therebetween with the plate 15a. 
A space between an inner circumference of the top plate 17 and the center pole 15b forms a magnetic gap 19 in which the voice coil 12 is disposed.
An opening 9a through which the voice-coil bobbin 11 is penetrated is formed in a center of the diaphragm 9. The edge 7 connected to a peripheral edge of the diaphragm 9 is fixed to the diaphragm supporting portion 5a in such a manner that a mounting flange portion 7a provided along an outer circumference of the edge 7 is caught between the diaphragm supporting portion 5a and a ring-shaped gasket 21 stuck to the diaphragm supporting portion 5a. An inner circumferential portion 9b of the diaphragm 9 which forms the opening 9a is fixed to a periphery of the voice-coil bobbin 11 penetrated through the opening 9a by adhesion or the like.
A dust cap 23 is stuck to a central portion of the diaphragm 9. This dust cap 23 covers a front end of the voice-coil bobbin 11 to prevent dust or the like from entering the magnetic gap 19.
The cylindrical voice-coil bobbin 11 is loosely fitted on the periphery of the center pole 15b in an axially movable state, and is elastically supported on the frame 5 by means of a damper 25 so that its axial movement is restricted.
In general, a damper in which a corrugated structure is formed concentrically with respect to the voice-coil bobbin 11 is widely used as the damper 25 (refer to, for example, JP-A-63-155900 and JP-A-11-262085).
The damper 25 has a peripheral edge fixed to a damper supporting portion 5b of the frame 5 and an inner circumferential portion fixed to the periphery of the voice-coil bobbin 11, and restricts radial displacement of the voice-coil bobbin 11. In addition, while the diaphragm 9 is being driven, the damper 25 absorbs vibration energy of the diaphragm 9 by deformation of the corrugated structure, thereby performs vibration damping on the diaphragm 9.
The frame 5 generally has a structure in which openings 5c are arbitrarily provided between the diaphragm supporting portion 5a and the damper supporting portion 5b. These openings 5c serve as air holes for releasing back pressures when the diaphragm 9 is being driven, at the same time, serve to reduce a weight of the frame 5.
In the speaker apparatus 1, when an acoustic signal is input to the voice coil 12 via input terminals and lead wires (none of which is shown), the diaphragm 9 is vibrated by reciprocating vibrations of the voice-coil bobbin 11, thereby performs sound reproduction.